Ketamine reduces inducible superoxide generation in human neutrophils in vitro by modulating the p38 mitogen-activated protein kinase (MAPK)-mediated pathway.

Many cellular stresses and inflammatory stimuli can activate p38 mitogen-activated protein kinase (MAPK), a serine/threonine kinase in the MAPK family. The different stimuli act via different receptors or signalling pathways to induce phosphorylation of the cytosolic protein p47(phox), one subunit of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. Formyl-methionyl-leucyl-phenylalanine (fMLP) has been shown to induce the p38 MAPK phosphorylation during the respiratory burst in human neutrophils. Here, we show that treatment with S(+)-ketamine or R(-)-ketamine at different concentrations (50, 100, 200, 400 microM) reduced fMLP-induced superoxide anion generation and p47(phox) phosphorylation in neutrophils in a concentration-dependent manner (y = -0.093x + 93.35 for S(+)-ketamine and y = -0.0982x + 95.603 for R(-)-ketamine, respectively). While treatment with 50 microM ketamine inhibited fMLP-induced superoxide generation by 10%, treatment with 400 microM S(+)-ketamine and R(-)-ketamine reduced fMLP-induced superoxide generation to 60.5 +/- 8.3% and 60.0 +/- 8.5%, respectively, compared with that in neutrophils treated with fMLP alone. Furthermore, treatment with ketamine down-regulated both fMLP-induced p47(phox) and isoproterenol-induced p38 MAPK phosphorylation and superoxide production. Interestingly, treatment with SB203580, the p38 MAPK inhibitor, also mitigated fMLP-induced superoxide anion generation and p38 MAPK and p47(phox) phosphorylation as well as apoptosis in a concentration-dependent fashion in neutrophils. Therefore, ketamine racemes inhibited fMLP-induced superoxide anion generation and p47(phox) phosphorylation by modulating fMLP-mediated p38 MAPK activation in neutrophils.